A classic solution would be ...
Published by P.S. Dilipkumar, TATA CONSULTING ENGINEERS LIMITED - Consultant
A classic solution would be to use a pump as a turbine. With a little modification to the shaft arrangement (to protect from damage due to reverse rotation and over-speed due to load throw off), you'll have an economical solution. You should consult a reputed pump manufacturer who would give you all the information you need.